If it should not work as sensitive as new collodion, add one drop of aqua ammonia to each ounce of collodion as you use it. - J. R. Clemons.

You will find in practice that a soft, spongy collodion will always he highly sensitive, for the reason that its - mechanical constitution is such that the molecules of silver move more freely within and throughout it,- that is to say, with less friction - and rearrange themselves, by the action of the light, more readily than they do when enveloped in a tough or hard collodion. No doubt, a part of the success of the " acid bath " is due to these facts, for the great quantity of acid tends to make the collodion film peculiarly tender, velvety, and soft, and thus affords the most delicate gradations of light and shade. I will give the formulae for collodion and bath, such as I am now working, and will only say that, like all other formula?, they must be used with judgment. Chemicals, particularly soluble cottons, are not always uniform, and the formula? must be modified to suit varying conditions. For general work, I use collodion made as follows:

Alcohol,........................................................

9 ounces

Ether,............................

6 "

Soluble Cotton,............................

108 grains.

Iodide of Ammonium,............................

18 "

Iodide of Cadmium,............................

18"

Chloride of Calcium,............................

9 grains.

The nitrate of silver bath I make of nitrate of silver, twenty grains to the ounce of water, and for every two quarts of the solution add half ah ounce of C. P. nitric acid. The amount of acid used must depend upon circumstances; you will probably require more acid. I often use as much as two ounces, or more, with success, in two quarts of solution. To develop, I use from fifteen to twenty grains of protosulphate of iron to the ounce of water, with enough acetic acid to cause it to flow smoothly. - J. "W. Black.

171. Foggy lines or streaks, in the direction of the dip, on negatives often appear after freeing the nitrate bath from organic matter, or strengthening with new silver. I am not aware that any remedy has been proposed for this trouble, except moving the plate horizontally in the bath for the first thirty seconds after immersion, which had scarcely any appreciable effect in my case. I was induced to give this some consideration through having about one hundred and sixty ounces in this condition, although free from organic matter, and sufficiently acid. My other bath working well with the same collodion, I inferred that the bath, having been continually strengthened with a stronger uniodized silver solution for a long time, had not the same amount of iodide in it when it was still further strengthened

172. Another defect is shown in the form of streaks and lines, starting at the lower edge of the plate end extending upward in the form of a triangle.These come from ascam to be found floating on the surface of the silver solution, If thedark - room is kept clean, the bath c when not in use, and the habit followed of filtering the solution day or two, this defect will rarely annoy you.

173. Dark, opaque lines running down from the top of the plate are also frequently met with. (Unequal or irregular development is their usual cause. If for any reason, a greater amount of silver is deposited upon one port of the plate than the other, these marks will occur. After with new silver and cleared from organic matter. I therefore added a few grains of iodide of potassium, and Altered, letting it stand all night. On trying it the following day the lines had entirely disappeared, the negative having all the beautiful bloom of one taken in a new bath. Before the iodide was added, the negatives were thin and weak, without body. -

Henry Gregson.

The bath will never "streak " the plates if the latter are moved about in the solution as soon as dipped, and kept in motion until smoothly coated. This is necessary more particularly when the bath is charged with ether and alcohol. The alcohol mixes with the solution, but the ether rises to the surface and sometimes causes scum. - Elbert Anderson.

172. A very common and often unsuspected source of streaks is the presence of scum on the surface of the bath, which, if the room is very dark, is not observed.

There are other causes of streaks and stains, but this is the chief. We mention it that the inexperienced photographer may see the necessity of carefully overhauling the whole of his operations when he meets with any of these difficulties, and not fancy that, by making his dark-room so dark that he cannot move in it without upsetting something, he is forthwith to rid himself of further trouble in this respect.

Nevertheless, too much stress cannot be laid on the importance of excluding all actinic light from the dark-room. The more perfect the working condition of the chemicals, the more dangerous will necessarily be every stray beam of white light. - Old Argentum.

178. A network appearance on the film after developing, when universal, and accompanied by rottenness of film, often depends upon the use of collodion containing water. Or, if not due to this cause, the plate may have been immersed too quickly in the bath, and the soluble pyroxylin partially precipitated. This is very likely to happen when using collodion containing a sufficient excess of alcohol to interfere with the setting properties of the pyroxy-lin, especially in cold or damp weather. - T. Frederick Harkwich.

Surface stains are a botheration wherever occurring. One great cause is too long a time between the sensitizing of the plate and its exposure to the light; but there are many others. The way to prevent them is what we want to know; the cause we need not care for, though that often rules the cure. The shields should always be kept clean, and a good plan is to interpose strips of blotting-paper between them and the plate. All varnishes which have any action whatever on nitrate of silver should be avoided. In case of long exposure the dark slide should be wrapped in a thick, damp cloth, and, as far as possible, when the plates must be long kept, use a new nitrate bath, or one nearly new. Very often these stains can be 9 the developer is flowed over the plate and the image begins to appear, if the plate is held vertically, the developing solution will, left to its own action, form in irregular lines, and carry in its train more silver upon some parts than others, thus causing the uneven development spoken of, and the consequent lines or streaks.